FIG. 1 illustrates the general layout of a circuit, showing a three-phase grid 11 that is connected via a transformer 12 to a converter 13 to which, in turn, a single-phase grid 15 is connected via an additional transformer 14. The converter 13 is configured with converter stages 16, 17 to which a direct voltage (DC) intermediate circuit 18 as well as an absorption circuit 19 are connected. The absorption circuit 19 is normally adapted to twice the nominal frequency of the single-phase grid 15 and can therefore absorb the pulsing power output of the single-phase grid 15. If this absorption circuit 19 is omitted, the DC intermediate circuit 18 must absorb the pulsing power output and must have a corresponding layout.
One embodiment of such a circuit is described in the publication “NEUE BAHNSTROMUMRICHTER FUER DIE DB IN LEHRTE UND ASCHAFFENBURG” (New Traction Current Converters for the German Railroad (DB) in the cities of Lehrte and Aschaffenburg), published in: Elektrische Bahnen, Journals 4+5/2009. The three-phase grid described therein is the public power grid with 50 Hz, 110 kV and the single-phase grid is the railroad grid with 16.7 Hz and 110 kV. In that case, the absorption circuit has a frequency of 33.4 Hz. Four converter stages are provided on the railroad side, which respectively are connected to one winding of the associated railroad transformer. As a result, the output voltages of the converter stages are summed up in the railroad transformer.